CA1053870A - Method for sealing a plate dialyzer - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A method of sealing a diffusion device having symmetrical stacked plates and associated diffusion membranes covering a side of each plate, the plates having fluid flow channels from end to end thereof adjacent opposed plate edges comprises sealing an end of each channel in each stacked plate, encasing the plates and membranes in a pair of hollow shells to enclose the plates, the shells defining peripheral flanges which abut one another when assembled, and molding about the outer periphery of the flanges a unitary integral retention member. The shells and flanges are held together until the retention member has hardened so that the member will hold the flanges together in firm, abutting relation.

Description

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~053870 -This invention relates to a plate dialyzer with membranes located between the plates.
Dialyzers have an extensive field of use. They are used for separating solvent-containing liquids, particularly for separa-ting colloids from molecularly dispersed smaller substances which are contained therein. When differently constructed, these plate dialyzers can also be used for exchange between liquids and gases, for example, as artificial lungs; for gas exchange, for example, as artificial gills; or as heat exchangers between two media capable of flowing, depending upon the selection of the membranes which separate the media taking part in the material exchange or heat exchange.
A special field of use for platc dialyzers is that of extra-corporeal hemodialysis. In that case, the semipermeable mem-brane takes over the task of the physiological filter of the glomerulus capillaries. According to the laws of osmosis and diffusion, an exchange of material then takes place between, on the one hand, a blood film applied to one side of the membrane and, on the other hand, a scavenging solution flowing past the other side of the mem-brane. This use of a plate dialyzer as an artificial kidney is becoming more and more important at the present time, and for that reason, hereinafter special reference will be made to a blood dialyzer. However, the devices of this invention are also intended for use as blood oxygenators and for other uses not involving blood.

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An ob~ect of the pre~ent invention i8 to eliminate drawbacks of prior art constructions through the provision of a plate dialyzer of greatly simplified construction which provldes improved diffusion characteristics by improving the flow characteristics of blood and dialysis solution passing through the device, and providing ease and reliability of manufacture.
This application is a division of copending Canadian application Serial No. 190,162 filed January 15, 1974.
The invention as defined in the above-identified parent application provides, in a diffusion device, a stack of plates separated by semi-permeable membranes to provide a pair of separated, isolated flow paths through the diffusion device on opposite sides of the membranes, the plate having a membrane-supporting profiled surface comprising a plurality of rows of upstanding pro~ections, in which the membranes are disposed across the plates over the pro~ections while stretched in one direction, the spacing of the centers of the projections in rows in the general direction of stretching being greater than the center-to-center spacing of the projections in rows trans-verse to the general direction of stretching to prevent undue sagging of the membrane upon wetting in the transverse direction while permitting lo.w flow resistance across the plates, the surface also comprising a plurality of support ridges extending in continuous, uninterrupted fashion across the plate in the general direction of the flow paths to abut corresponding support ridges on a~ ad~acent plate of the stack to control tha spacing between facing plates.
On the other hand the invention of this application ~ 3 dapl~

: ` 10538~0 provides, the method of sealing a diffusion device comprising a plurality of stacked plates and associated diEfusion membranes covering a side oE each plate, in which the plates have fluid flow channels running from end to end thereof adjacent opposed plate edges, the plate being symmetrical and the channels extend-ing through opposed plate ends to communicate therethrough which method comprises: sealing one end of each channel in each stacked plate, and thereafter encasing the stacked plates and membranes in a pair of hollow shells which cooperate to enclose the plates, the shells each defining peripheral flanges which abut one another in assembled, stack-enclosing position; and thereafter molding about the outer periphery of the flanges a unitary, integral -:
retention member, and holding the shells and flanges together until the retention member has hardened, whereby the integral retention member holds the flanges together in firm, abutting relation.
~ The present invention also may be defined as a diffusion .
device comprising a plurality of stacked plates and associated diffusion membranes covering a side of each plate; the plates having fluid flow channels running from end to end thereof adjacent opposed plate edges; the plates being symmetrical and the channels extending through opposed plate ends to communicate therethrough;
one end of each channel in each stacked plate being sealed; the stacked plates and membranes being encased in a pair of hollow shells which cooperate to enclose the plates; the shells each defining peripheral flanges which abut one another in assembled, stack-enclosing position; and a molded unitary integral retention member positioned about the outer periphery of the flanges, the integral retention member holding the flanges together in firm, abutting relation.

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1~53~70 In the drawings, preferred embodiments of this invention are illustrated. The particular embodiments are improvements on the dialyzer disclosed in United States Patent ~o. 3,730,350, and except as otherwise indicated hereln, can be manufactured in accordance with the teachings of that patent.
Figure 1 is a perspective vlew of a preferred embodiment of the dialyzer of this invention :in an intermediate state of manufacture of the casing.
Figure 2 is an enlarged, partial side elevational view, taken partly in section~ of the dialyzer of Figure 1 after complete assembly.
Figure 3 is a full side elevational view with portions broken away of the dialyzer of Figure 1 after complete assembly.
Figure 4 is a diagrammatic view showing the relationship of 2 plate used in the dialyzer of Figure 1 and its overlying membrane, and the respective typical flow paths of dialysis solution and blood.

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Flgure 5 i8 a plan vlew of a preferred plate design uaed ln the dialyzer of this lnvention.
Figure 6 is a diagrammatic view of a stack of plates and associated me~branes.
Figure 7 (appearing on the same sheet of drawings as Figure 1) is a sectional view taken along line 14-14 of the stack of plates of Figure 6, with the respective parts slightly vertically separated for purposes of clarity.
Figure 8 is a partial, greatly enlarged plan view of one corner of the plate of Figure 5.
Flgure 9 i~ a plan view of anoth&r preferred embodi-ment of a plate for use in this invention.
Figure 10 is a greatly enlarged perspective view of a portion of the edge of the plate of Figure 9 and a fragment of overlying membrane.
Figure 11 is a greatly enlarged plan view of one corner of the plate of Figure 9.
Figure 12 is a transverse sectional view of another embodiment of a dialyzer essentially identical to that of Figure 1, but with a different plate design.
Figure 13 is a dia~rammatic plan view of one corner of the stack of plates of the device of Figure 12, showing in phantom how ridges of an ad~oining facing plate sre positioned wlth resp~ct to the ridges of the plate shown.
Figure 14 is a sectional view taken through the plates of the device of Figure 12, shawing the relationship of the membranes and respective ridges of the plates.
Figure 15 (appearing on the same sheet of drawings as Figure 12) is an enlarged transverse diagrammatic sectional view showing the shape of the blood manifold in the device of Figures 1 and 12.

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Plgure 16 (appearlng on the same sheet of d~awings as Flgure 12) i8 a fragmentary plan view of the ln31de corner of a shell used to enclo~e the plates ln the de~ice of Flgures 1 and 12.
Flgure 17 (appearlng oll the same sheet of drawlngs as Flgure 13) i3 an elevatlonal vlew, taken partly ln sectlon, of a modlfled dialysis of this lnventlon.
~ he stacked plate diffusion device of this applica-tion is particularly capable of exhibiting a high efficlency of diffus~on, so that liquid such as blood passed through the device can be essentially completely processed by a single pass through the device. This is accomplished because the device of this invention can be designed with an extremely thin flow path for blood, since the profiled surface on the stack of plates may have flow channels which are no more than 0.5 mm. and even less in depth. Also, the dialyzer of this inventlon can be fabricated in a manner suitable for supporting ultrathin membranes, which will accelerate the diffuslon process in a manner unavallable to the designs of the prior art.
Referring to the diffusion device of Figures l through 9, a stack of plates and membrances is assembLed in the manner generally tescribed in U.S. Patent No. 3,730,750, and then placed between a pair of hollow shells 30, 32 which may be of molded plastic. Shells 30, 32 face together to define a chamber inside, the parting line between the t~o shells being bracketed by a pair of flanges 34, 36.
Prior to insertion of the stack of plates and ~ -~embranes (portions of which are illustrated in Figure o), the stack of plates is compressed, desirably at a pressure of about 14 to 28 kg. per square cm., to cause the facing rear sldes of the plat~s and the membra=e ends between them tap/,~

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to become pressed together, to prevent the passage of significant amount~ of fluid between the facing rear sides. The above pre~sure values are particularly effective for rectangular plates having a length of about 12 cm. and a width of about 6 cm., being about 1 mm.
in thickness, and being made of polystyrene plastic with adjoining ultrathin membranes of about 10 rnicrons thickness. When the above dimensions are significantly varied, the optimum pressure on the stack of plates and membranes to achieve the desired effect above may also change.
The stack typically has been about 100 and 150 separate plates and overlying membranes.
A relatively thick pressure plate 37 is placed at each end of the stack of plates, preferably prior to the pressure step, for pro-tecting and positioning the plates, and to uniformly distribute the compressive pressure placed on said stack in the pressure step and thereafter by said casing.
After the pressure step on the stack of plates and membranes, they are placed inside hollow shells 32, 34, along with spacers 370 and the shells brought together under pressure so that flanges 34, 36 are in facing contact with each other as shown in Figure 8. Groove and 0 ring system 35 (Figures 1 and 15) is disposed around manifold chamber 44 and the corresponding outlet manifold chamber, for sealing purposes.
Flanges 34, 36 can then be sealed together by any convel~tional means. It is preferred to injection mold a frame of plastic 38 (Figures 2 and ~ ~ about the periphery of flanges 34, 36 to enclose the peripheral portions of the flanges and to permanently bond them together in firm, abutting relation. Figure 17 al~o shows an identical frame 38 as applied to a pair of modified shells.

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- Ridgeu 40 arc formed ln sectior~ of flanges 34, 36 to retain the molded frame 38 in tight-fitting relationship. Another ~et of ridges (not shown) are typically placed on nange portions 41 on the other side of the dialyzer.
Typically, blood enters the device of Figure 1 through port 42, and is distributed by way of manifold chamber 44 (Figure 15) along the side edge surfaces of the stacked plates and membranes through the beveled manifold areas 46 (Figure 6) of the plates which function in the manner of connecting chambers 10, as shown in Figure 3 of U. S.
Patent No. 3, 370, 350. Manifold chamber 44 decreases in depth in all directions as it radiates from inlet 42, and terminates with a spacer ridge 50, to position the plates 52. Alternatively, an outer portion of chamber 44 can be in actual contact with plates 52, with the shells 30, 32 being sufficiently flexible to expand slightly when pressurized as blood entsrs inlet 42, so that a flow channel having a depth of a few microns or qo is formed by the pressure. The advantage of this is that the vol~me of blood contained in the device is brought to an absolute minimum, which is desirable. Otherwise, the minimum depth of chamber 44 can be about l mm. or less while in unpressurized condition.

The reduction of the depth of manifold chamber 44 in a manner dependent on its distance from inlet 42 also assists in the distribution of blood or other fluid across the sides of plates 52 in a manner which corresponds to the demand for fluid passing between the plates, reslllting in improved uniformity of flow with a minimum of blood volume in the device.
The optimum flow of blood or other fluid through manifold cham-ber 44 is combined with a minimum blood volume in the manifold cham-ber when the manifold chamber defines a generally uniforIn curve in all directions which approximates the following: d--- D 2/ 2~ + C-10538~7~
d (Figure 15) is the depth of all points of chamber 44 along lines 43 which extend radially from the peripheral wall 45 of fluid port 42 to meet a line. in perpendicular relation thereto, constituting an extension of a peripheral edge 47 of chamber 44. do is the depth of the manifold chamber directly underneath peripheral wall 45 multiplied by the circumference of port 42; S is the distance of the point measured along a said perpendicular line 43, measured from wall 45; S0 is the total distance along line 43 from wall 45 to the peripheral edge 47 of said manifold; and C is the minimum desired depth of manifold 44 at peripheral edge 47.
C is preferably about 0. 5 to 1 mm. while, for a dialyzer of the specific type described herein, d 0 is suitably about 0. S sq. cm., and S0 about 3 cm. for a dialyzer having about one hundred eighteen 12 cm.
by 6 cm. by 1 mm. plates made of polystyrene plastic and having adjoining ultrathin membranes of about 10 microns thickness.

Blood from manifold chamber 44 passes between facing rnem-branes of adjacent plates, and then is collected in a manifold chamber defined by shell 32, which is similar in structure to chamber 44. The blood is then conveyed from the device by outlet 54.

Dialysis solution (or oxygen, if the device is intended for use as a blood oxygenator~ can enter the device by inlet 56, where it enters a manifold space 60 (Figures 3, 15, and i6) for distribution of the diabsis solution to the ends of the stack of plates 52. The dialysis solution then passes into plate inlet ports 62, which constitute a groove .

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defined in the back side of each plate which is open to ends 64 of each plate. Thus dialysis solution passes into the plate stack without disruption of sealing shoulders 66.
Inlet ports 62 extend through sealing shoulders 66 a distance sufficient to insure adequate sealing of the ends of the plates. A hole 68 passes entirely through each plate 52 to serve as a connection between inlet port 62 and flOw channel 70. Channel 70 is a groove inscribed in the front side of each plate for the distribution of dialysis solution across one side of the plate.
The dialysis solution then passes from flow channel 70 across profiled surface 72 to a second fLow channel 74 (Figure 5 ) for collection of dialysis solution.
The second flow channel then communicates with plate outlet port means 76, which is typically identical in design and function to inlet port 62 and hole 68.
As is seen from Figure 5, each plate 52 is symmetrical in its initial condition, having ports communicating with the exterior at both ends of flow channels 70 and 74. This simplifies the assembly of the stack OI plates, since they can be placed together in face-to-face relation without as much concern about assembly accuracy as is required when -asymmetrical plates are brought together in face-to-face relation.
After the plates have been assembled in a stack, the respective second open ends 78 of channels 70, 74 are heat sealed with a hot bar or otherwise occluded, as at 78a in Figure 2, so that channels 70, 74 are open at only ports 62, 76. This heat sealing step is typically per-formed after the pressure squeezing step described previously, but b~fore the stack of plates is placed inside of shells 30, 32.

_ g _ 1~S3870 Small support plates 79 are placed at each end of plates 52 to preverlt the dialyzate manifold spaces 60 at each end of the plates fn~m collapsing under the pressures cncountered during the injection ~nolding step which creates frame 38 for s~aling the shells together.
Figure 4 shows schematically the blood flow path 49 running transversely across plate 52 and separated therefrom by membrane 39, while the dialyzate flow path 80 is shown to pass into the plate by inlet port 62 and to move as previously described.
Profiled surface 72 of plate 52 is shown in Figure 8 to con-stitute rows of upstanding projections 82 which are typically generally pyramidal structures having a height of 0. 05 to 0. 5 mm.; for example, 0.15 mm. projections 82 cover most of the plate. Preferably, the alternate rows of projections are laterally shifted with respect to their adjacent rows, so that both blood and dialysis solution flow in crossing grooves B3 running between dialysis iluid flow channels 70, 7~, for improved gentle mixing of both the blood and dialysis fluid as it passes across the plate face.
The centers of these projections are spaced a distance D1 of about 0. 3 to 1. 5 mm. apart in the rows which are transverse to the - 20 general direction of blood flow 81 across the plate ~ace, and generally parallel to flow channels 70, 74, to provide narrow grooves 83.
The advantage of this is particularly found when ultrathin mem-brane of no more than about 20 microns thickness is used, in that the great multitude of tiny and closely spaced projections provides adequate support for the thin membrane, preventing the membrane from ripping, or from sagging into the flow channels between the projections, Thus, .. . . .

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since this plate structure permits an ultrathin membrane to be used, the diffusion rate between fluid passing on opposite sides of the mem-brane is substantially improved over the known and conventional diffusion membranes, which are substantially thicker.
The flow resistance across plates 52 is reduced by spacing the centers of the projections 82 in rows extending parallel to the blood nOw direction 81 a greater distance apart than the spacing in the trans-verse rows described above. This spacing D2 is typically about two to three times the distance D1, that is, about 0. 5 to 5 mm., preferably about three times that of D1. A preferred spacing Dl is 0. 5 mm., while a preferred spacing D2 is 1. 5 mm. .
Pyramidal projections 82 are typically about 0. 5 mm. long on their long axis and 0. 2 to 0. 3 mm. long on their short axis as shown in Figure 15.
It is preferred for the dialysis membrane to be placed across the plates 52 and projections 82 while stretched in such a direction that the center-to-center spacing between projections 82 in the stretched direction of the membrane is greater than the center-to-center spacing of the projections transverse to the stretched direction of the membrane. In other words the membrane, which is typically a cellulose-based membrane for blood dialyzers, is laid across plate 52 while being gently stretched in a direction generally parallel to direction 81. As stated above, the projection spacing in a direction perpendicular to direction 81 is about one-third the distance of the projection spacing in direction 81.

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Tho Qdvantageof this is that, when wetted, cellulose-based dialysis membranes and the like tend to expand, and the degree of expansion in the direction perpendicular to their stretched direction i8 greater than in their stretched direction. If the degree of expan-sion of the wetted membrane is too great, it will sag and occlude the dialyzate flow channels 83 between the projections 82. Thus, pro-jections 82 are spaced more closely together perpendicular to direc-tion 81 to account for this increased degree oE sagging of the membrane.
If the membrane is stretched onto the plates in a direction transverse to direction 81, the spacing of projections 82 can be modified accord-ingly to prevent undue membrane sagging.
Ridges 84 are positioned to mate with corresponding ridges on the faces of adjacent plates to serve as spacer members, thus preventing the projections 82 on facing plates from collapsing between each other during the squeezing or pressurization step of the stack of plates.
Figure 16 shows a portion of the inside view of shells 30, 32.
Dialyzate inlet tube 56 is shown solvent-sealed in position in an appro-priate receptacle for the inlet port. Spacer ridge 50 is shown in position to space the plates in uniform manner.
Referring to Figures 9 through 11, an alternate plate embodi-ment 85 is disclosed having a profiled surface comprising proJections 86 (Figure ll ). Plate 85 has a pair of sealing shoulders 88 in a manner similar to the previous plates, but with several dialysis fluid entrance ports 90, which are grooves defined on the rear side of plate 84 in a manner similar to that shown in Figure 8 as inlet 62. Holes 92 corres-pond to holes 68, and four dialyzate channels 94 convey dialysis solution, - . :, . . - : , - . ~ - . . : : .

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~ i3870 extending transversely to the crossing grooves 87 defined by projec-tions 86 across plate 85. Channels ~4 are of differing length to pro-vide uniformly distributed dialysis solution to the space between each plate and its associated membrane. The arrangement insures that adequate supplies of dialysis solution are provided to the areas of plate 84 which are remote from entry ports 90. If desired, projec- `
tions 86 may be spaced in the arrangernent as shown in Figure 8 .
Correspondingly, a plurality of take-up channels 96 are pro-vided to convey flùid away from the plate by means of holes 98 which ~ ~
communicate with ports 100, defined on the back of plate 85, to permit ~ `
solution to be conveyed to the ex~erior without breaking the seal provided by sealing shoulder 88.

Tooth-like structures 102 are provided on one side of plate 85 as a means to provide a manifold chamber for blood. The blood is, as previously described, conveyed across plates 85 between associated membranes (one of which is shown as membrane 106 in Figure 10) and correspondingly expelled from the other side of plate 85.

In this embodiment, the plates are stacked so that tooth-like structures 102 of adjacent facing plates are located at opposite sides from each other. One set of the teeth 102 then will serve as an inlet manifold for the blood while the other set on the other plate will serve as an outlet manifold.
Support ridges 108 function in the same manner as ridges 84 (Figure 5 ) to prevent the projections 86 of plates in face-to-face relation from being forced together.
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~, . ., .. .... .. , . -,, ~ -~S~8~0 Referring to Figures 12 through 14, a longitudinal sectional vlew of a device similar to Figure 1 is shown having a modifled plate design. Blood enters through inlet 42 as before and departs through outlet 54. Dialysis solution enters through inlet 56 into manifold chamber 60, which is supported by blocks 7g, as previously shown, to prevent collapse of manifold chambers 60 during the injection molding of frame 38. Dialysis solution passes from manifold cham-ber 60 through a plurality of channels 110 defined on the rear side of each plate underneath sealing shoulders 112. Channels 110 communi-cate with holes 114, which pass entirely through each plate just adjacent the sealing shoulders 112 to provide access from channels 110 to the front side of the plate.
The majority of the plate is provided with alternating rows of parallel, short ridges 116, typically no more than 0.05 to 0.5 mm.
high, about 1 to 1. 5 mm. long, and substantially less in width (0. 3 mm. ), in which the ridges of alternating rows define angles to the ridges of adjacent rows. Preferably, all of the short ridges 116 define acute angles to the edges of their respective plates between the sealing shoul-ders 112, and an odd number of rows of short ridges are provided on lthe plate in at least one, and preferably bath directions, so that the short ridges 116 of plates disposed in face-to-face relation are in abutting, angular relation to corresponding ridges 116' of the adjacent face-to-face plate, to provide spacing and support between the plates.
This i9 illustrated in Figure 14, in which a pair of adjacent membranes are shown to be retained and held together by crossing ridges 116, 11~' of adiacent plates. The phantomed ridges 116' of Figure 20 illustrate the same principle. When crossing ridges 116 are used, the long ridges 84 ~Figure 5 ) are no longer necessary, and more uniform plate - . . . ~ . . , ~ . , - : . - : : , 1~5~7a~
support is provided. Dialysis solution is then collected in corres-ponding collection channels 118 (of identical structure to members 110, 114), which solution is then withdrawn through another manifold 60 and outlet 57.
In T~'igure 12, ridges 116 ar~ shown enlarged and with fewer rows than would be customarily used, for purposes of clarity. A
typical ridge spacing 117 between ridges of adjacent rows is about 0.2 mm.
P~eferring now to Figure 17, a modified device of this inven-lû tion comprising a pair of shells 120, 122 is disclosed. Blood inlet 54 is essentially the same as in Figures 1 and 12, as is blood outlet 42, frame 38, and an exemplary stack of plates and membranes having ridges 116 and functioning as described above. However, -the dialysis solution inlet and outlet have been moved with respect to the casing of Figures 1 and 12 to avoid the molding problems which result when the dialysis inlet and outlet are involved with the molding opera-tion of frame 38. Thus, new dialysis inlet 124 is located below frame 38, while dialysis solution outlet 126 is located above frame 38.
Dialysis manifold chambers 128 are provided, corresponding to mani-fold chambcrs 60 in Figures 12 and 15, but having sufficient depth and volumc to climinate any possiblc nonuniformity of flow caused by the asymmetric locations of inlet 124 and outlet 126.
It can be seen that shells 120 and 122 can be manufactured from the same mold, and assembled simply by facing the two shells in opposite direction during assembly.
The above has been offered for illustrative purposes only, and is not to be considered to limit the invention, which is defined in the claims below.

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Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. The method of sealing a diffusion device comprising a plurality of stacked plates and associated diffusion membranes covering a side of each plate, in which said plates have fluid flow channels running from end to end thereof adjacent opposed plate edges, said plates being symmetrical and said channels extending through opposed plate ends to communicate therethrough which method comprises: sealing one end of each channel in each stacked plate, and thereafter encasing said stacked plates and membranes in a pair of hollow shells which cooperate to enclose said plates, said shells each defining peripheral flanges which abut one another in assembled, stack-enclosing position; and thereafter molding about the outer periphery of said flanges a unitary, integral retention member, and holding said shells and flanges together until said retention member has hardened, whereby said integral retention member holds said flanges together in firm, abutting relation.

2. The method of claim 1 in which said unitary integral member is an injection molded frame of plastic which encloses peripheral portions of said flanges.

3. The method of claim 1 in which, prior to said encasing step, said stack of plates is compressed to pressure weld the plates and membranes together into a compressed, generally unitary stack.

4. The method of claim 3 in which said membrane is no more than 20 microns in thickness.

5. The method of claim 4 in which said stack of plates and membranes is compressed at a pressure of about 14 to 28 kilograms per square centimeter.

6. The method of claim 1 in which opposed ends of each channel adjacent opposite edges of the plate are sealed.

7. A diffusion device comprising a plurality of stacked plates and associated diffusion membranes covering a side of each plate; said plates having fluid flow channels running from end to end thereof adjacent opposed plate edges; said plates being symmetrical and said channels extending through opposed plate ends to communicate therethrough; one end of each channel in each stacked plate being sealed; said stacked plates and membranes being encased in a pair of hollow shells which cooperate to enclose said plates; said shells each defining peripheral flanges which abut one another in assembled, stack-enclosing position; and a molded unitary integral retention member positioned about the outer periphery of said flanges, said integral retention member holding said flanges together in firm, abutting relation.

8. The diffusion device of claim 7 wherein said hollow shells hold the stacked plates encased therein in compressed relation to each other.

9. The diffusion device of claim 7 wherein opposed ends of each channel adjacent opposite edges of the plate are sealed.